The adsorption of sodium dodecyl sulphate at the mercury electrode and its effect on the electrochemical processes of cadmium(II) in sodium chloride solution

Abstract

The adsorption of sodium dodecyl sulphate (SDS) at the mercury electrode in 0.55 mol dm −3 sodium chloride has been studied on the basis of capacity measurements using ac polarography. Investigations were carried out in a wide concentration range of SDS (3.8 × 10 −7−1.9 x 10 −3 mol dm −3) at the dropping mercury electrode (DME) and at the hanging mercury drop electrode (HMDE) with a prior accumulation of surfactant at the potential E = −0.6 V vs. SCE. The effect of SDS upon the electrode reaction of cadmium was studied by differential pulse polarography. The rate constant of the electrode reaction of cadmium, k s, was estimated from the shape and the height of differential pulse polarograms using theoretical curves obtained by digital simulation. It was found that association processes both in the bulk solution as well as at the electrode surface play an important role in the adsorption and inhibition processes of SDS. An inhibition effect for cadmium is considerably decreased at the HMDE and at bulk concentrations near to the CMC value.